Automatic telephone system



June 9, 1925. 1,541,400

J. SAVIN AUTOMATIC TELEPHONE SYSTEM Filed Jan. 12, 1921 2 e -She 1 nusfiZuf- JuZm 552ml June 9, 1925. 1,541,409

J. SAVIN AUTOMATIC TELEPHONE sysmsm Filed Jan, 2, 1921 2 Sheets- Sheet 2 Juhn 55mm Patented June 9, 1925.

barren STAT-ES. Parent OFFICE.

JOHN savrn, or LIVERPOOL, ENGLAND, ASSIGNQR TO auroiaarro ELECTRIC M Party, or or-ncaeo, ILLINOIS,

A CQR-FORATION OF ILLINOIS.

AUTOIVIATIC TELEPHONE SYSTEMI.

Application filed January 12, 1921. Serial No. 436,664.

To a?! 1071 out it may concern:

Be it known that 1, JOHN SAVIN, a subject of the King of Great Britain and Ireland, and a resident or" Liverpool, England, have invented certain new and useful improvements in Automatic Telephone Systems, of which the "following is a specilication.

The present invention relates in general to automatic telephone systems in which connections are established through the medium of mechanical switching devices at the exchange, but is more particularly concerned with systems or" this type which are of small capacity, such as are commonly used in the so called private branch exchanges. The present invention may be considered as being an improvement on or a modification of the system shown in the pending application of Winfred T. Powell, Serial No. 161,957 liled April 1%, 1917.

The object of the present invention is to provide a simple and inexpensive automatic exchange, capable of dealing with up to 10, lines or more, without involving the use of large capacity switches such as the 100 line connectors used in the Strowger automatic telephone system.

According to the present invention, two step by step switches of the type, having no release movement, that is to say, of the type in which every movement of the switch is controlled by the rotary stepping magnet, are linked together in such a manner, that one of said switches is adapted to act as a linder switch to move from the'line of the party previously using the switch, to the line of the next party calling, and establish connection therewith, while the other switch is adapted to act as a connector to establish connection under the control of the calling party with the line of the party required, and subsequently to move to a normal position corresponding to the position from which it started, under the control of its own stepping magnet, on the completion of the call.

Further features of theinvention will be better understood by referring to the accompanying drawings, in which, Figure 1 shows a diagram of connections oi? the callingv side of the exchange illustrating the arrangect tinder switches and the grouping h ci-ibers, Figure 2 shows a circuit diamm for operating the connector to establish the connection desired, while Figure 3 is a diagramn' atic representation of the num bering scheme of" the exchange system described.

It will be assumed that substation A is making a call, to do this he lifts his receiver 1 thereby closing the following circuit: earth, armature 2 of relay 3 and its resting contact, resting contact of armature i of relay 5 and said armature, line 6 to'substation A andback through line 7 to armature 8 and its resting contact, lower winding of relay 5, windings 9 and 10 of relay 11 to battery. In this circuit relay 11 energizes and short circuits its high resistance winding 10 at is arn'iature 12 and connects battery to the relay 13 by its armature 14-. Relay 1.3 energizes and connects earth. at its armature 15 to the starting wire 16 of the finder switch B, whereby it the switch is free, the relay 3 is energized. Armatures 2 and 17 and 18 are thereby operated, the former to connect earth to one side of the winding of high resistance relay 19, the other side of which relay is connected to the stepping magnet 20,'while armature 17 connects the junction of the stepping magnet 20 with relay 19 through armature 21 and its resting contact to private wiper 22 or the finder sufliciently to cause the armature 23 to move fronr its resting to its working Contact. The armature 3 is controlled by a. lighter spring than the other armatures & and 8 of relay 5 so that these latter armatures are not afiectedby this current. The consequence of this arrangement is that if the wiper 22' is not resting on the contact oil the calling line, which would only be the case if the calling man had been the last to use that switch, it will be earthed so that the high resistance relay 19 will be short circuited and the stepping magnet 20 will operate This will continue as long as the wiper 22 is earthed but as soon as it reaches the line of the calling party, earth will be missing and as the relay 19' is nolonger short circuited, it will operate in series with the magnet while the magnet 20" will not operate on account of the high resistance of relay 19. Relay 19 on operating connects wipers 2 1 and by means of its armatures 26 and" 27 to the upper and lower winding respectively of line relay 28 of connector switch C (Figure 2), which relay energizes in the following circuit, earth, lower winding of relay 28, armature 27 and itsworking contact, wiper 25, line 6, sub station A, line 7, wiper 24, armature. 26 and its working contact, upper winding of relay 28 to battery. Armature 29 of this relay connects earth to the winding of relay 30 which-energizes and at armature 31 connects earth back over line 3% to armatures 32 and 35 of relay 19 to maintain relays 36 and 19 energized after relay 3 has ecenergizcd. Relay 36 which energized originally on the energization of relay 19 through the circuitearth; armature 2 and its working contact, armature 32 and its working contact, armature 35 and its working contact, relay 3G tobattery, disconnects the starting wire 16 fromrelay 3 and transfers it on the deenergization of said relay through armature 18- to the starting wire 37 leading to the next finder switch. Armature 21 of relay 19, on said relay energizing connected earth to wiper 22 and thence through a 'mature L3 and its working contact to private normal 38 and to the upper winding of relay 5. In this circuit relay 5 operates fully and disconnects the lower winding of relay 5 and relay 11. 'Relay 11 deenergizes, some-what sluggishly in view of its winding 10 being short ci-rcuited, and at armature 1e breaks the circuit of relay 13 and disconnects earth from the starting wire, prior to the (issuergization of relay 3 and therefore before the starting wire 16 is connected through tostarting wire 37 of the next switch.

Before proceeding with the description of the connector switch C, a description will first-be given; of the grouping of the substations with relation to the finder switches.

For convenience, it will be assumed as shown in the system illustrated, that the capacity of the system is 39 local lines and four exchange lines while the finder switches have a capacity of 25 lines.

It should be mentioned that the connector switches which are of similar construction to the finderswitches, have two banks, each having a capacity of 25- lines. These twobanksare wiped over by two sets of wipers driven by a common motor magnet and preferably arranged on the same shaft. As one bank of the connector switch can deal with 21 local lines, and the other bank can deal with 18 local and 1 exchange lines, as indicated in the diagrannnatic numbering scheme, Figure 3, it is convenient to divide. thefinde'r switches into two groups one tor the former and the other for the latter set of lines. The number of finder switches provided for each set of lines will, of course, depend on the traffic requirements. For convenience, it will be assumed that two finder switches are sufiicient for each set of lines. These lines would in turn be divided into groups, for instance,tcn substations being normally allotted to one finder switch and eleven to the other in the first set, although obviously the arrangements may be modified as desired. The advantage of this subdividing is that usually subscribers of one group would use one switch, while subscribers of the other group would use the other switch, although in cases of two subscribers of one group requiring finder switches at about the same time, the last subscriber would be able to utilize the finder switch normally associated with the other group. Consequently, it when subscriber it had made a call the line finder B was in use, the starting wire 16 would be connected viathe working contact of armature. 39 of relay 36, resting contact of armature 18 to starting wire 37, resting contact of armature 39 of relay 36 of finder switch B to relay 3 to set this switch in operation. It finder switches Band B were both engaged simultaneously the. call would be held up, but in order that the number of times this occurs may be tween tained, a relay 10 is provided which energizes on the simultaneous energization of relays 36 and 36 through the circuit, earth, armature 4:1, armature t1, relay 40 to battery, and thereby closes the circuit through armature 4:2 and its working contact to meter e3. If this occurs frequently, it indicates that an additional finder switch is required.

If a subscriber in the group allocated to finder switch, B should make a call when said switch is engaged, the starting wire circuit is transferred through workingcontact oi? armature 39 of relay 35 through resting contact of armatiu'c 18 of relay 3 to starting wire 16 of finder switch B.

It should be mentioned that relays 11 and 13 are common to the group of substations allocated to finder switch l3, while relays 11 and 13 are common to the group of substations allocated to finder switch 13, while relay 5 is the cutofi relay of a substation ot the same group as substation A.

Having described the various arrangements controlling the connection of the calling subscriber to the finder switch, a dc scription will now be given of the circuits governing his connection to the party he desires.

Assume he want connection with substation 106, he will first operate his dial switch to produce one interriugtion, that isto say, the relay will be deenergiz d once, while lit) relay being of the slow to release type will remain energized. Consequently, a circuit will be closed from earth, through resting contact ofarmature 29, working contact of armature 44 of relay 30, series relay 45, armature 46 of relay 47 and its resting contact, armature 48 of relay 49 and its resting contact, magnet 50 to battery. Magnet 50 therefore steps the switch round one step from the. normal position shown. lViper 51 is thereby connected to earth, the first contact from normal in this bank being cart-lied. When the slow series relay 45 falls back a. short time after the transmission of the first digit, as the first digit was one, the following circuit will be closed, earth, wiper 51, arn'iature 52 of relay 45 and its resting contact, relay 53 to battery. Relay 53 operates and locks operated through its arinature 54 and its working contact to earth on armature 31 of relay 30; while armatures 55, 5G, 57 switch over from their normal connection to wipers 58, 59, 60 to wipers 61, 62, and 63 so that the lower bank of contacts is taken into use in place of the upper set.

Obviously if the first digit dialled had been other than 1, as the relay 45 remains energized throughout the trai'ismission of a series of impulses and as only the first contact from normal in the bank of contacts swept over by wiper 51 is earthed, it would be impossible for relay 53 to be energized and consequently, the upper set of wipers: would be taken into use. In order therefore, to obtain access to the lower bank, it is necessary that the number of the parties connected to that bank should lee-prefixed by the digit 1. The next digit to be dialled is O (ten impulses) and the circuit of the stepping magnet will be closed as before and the wipers will he stepped round ten more steps to the eleventh contact from normal. Figure 3 is a diagrammatic representation of the numbering scheme of the exchange system described. The left hand representation gives the position of the subscribers connections with their corresponding num bers in the upper bank of contacts and the right hand representation gives the. position of the subscribers connections in the lower bank of contacts. From these positions it. will be seen that the elexmnth contact corresponding to the number 10 is dead so that when the wipers come to rest on this contact, nothing happens and the subscriber can dial again. This time he sends six impulses, causing the stepping ma net to move the switch round so that private wiper 63 will make connection with private contact of substation number 106. Now if wiper (33 comes into engagement with an earthed Contact, the following circuit will be closed, earth, wiper ($3, resting contact of arn'iature 54 of relay 65 and said armature, working contact of armature 57 and said armature, armature 66 of relay 45 and its working contact, resistance 67, resting contact of armature 68 of ringing trip relay 69, upper winding of relay 49 to battery. Consequently, relay 49 energizes every time wiper (53 passes over an earthed contact. This is of no consequence during the transmission of impulses as relay 45 at armature 7O puts a. short circuit about the armature 48, but if the wiper 63 is resting on an earthed contact when relay 45 deenergizes after the transmission of a series of impulses, that is to say, if the party called is engaged, then the relay 49 will be locked energized through the contact springs controlled by armature 66, which are arranged to make contact before armature 65 breaks contact, working contact of armature 71 and said armature, working contact of armature 31 to earth; relay 49 at armature 72 connects the busy tone transformer 7 3 to one of the line conductors informing the calling subscriber that the line is engaged. The sub scriber then hangs up his receiver, thereby breaking the circuit of relay- 28 which deenergizes and is followed by the deenergization of relay 30. Relays 49, 53, 36, 19 and 5 also deenergize, due to the removal of the holding earth by armature 31 of relay 30f Amiature 31 also connects earth to all the contacts in the bank swept over by a wiper 74 except the first or normal contact, so that a circuit is closed for the stepping magnet 50 as follows, earth, wiper 74, magnet interrupter springs 75, resting contact of armature 89 of relay 65 and said arma ture, series: relay 45, armature 46 and its resting contact, armature 48 and its resting contact, magnet 50 to battery. Magnet 50 therefore. operates and continues to operate until the wiper 74 reaches the normal unearthed contact, that is to say, when the connector is in its home position, so that. both the finder switch and connector switch are in readiness for another call.

If, on the other hand, the party called was not engaged, there would have been no earth on wiper 63 and relay 49 would not be energized at the time relay 45 permitted its armature 66 to fall back. In this case the following circuit would be completed, earth, armature 31 and its working contact, armature 71 and its resting contact, upper winding of relay 47, resting contact of armature G6 and said armature, armature 57 and its working contact, armature 64 and its resting contact, wiper 63, winding of. cut-off relay of called line (see relay 5, Figure 1) to battery. Relay 47 and the cut-off relay of the called line energize over this circuit, the latter to cut-off the starting relay circuit while relay 47 looks itself energized at armature 75 to earth'on armature 31, closes the ringing circuit through the called station at armatures 76' and 77 and prevents further dialling affecting the stepping magnet by opening its circuit atarmature 46. The ringing circuit may be traced as follows,

earth, ringing generator 78, working contact of armature 7 9 of ringing interrupter relay 80, and said armature, resting contact of armature 87 and said armature, armature 7'6 and its working contact, armature 56 and its working contact, wiper 62, called subscribeflsline and ringer back to wiper 6i, armature 'and its working contact, armature 77 and its working contact, upper winding of relay 69 to battery.

Relay 69'is designed not to energize when the subscribe1."s receiver is onthe hook, but to energize immediately the receiver is removed, either with direct current alone or with direct current and ringing current together. Consequently, as soon as the called party lifts his receiver, relay (5%) energizes, and disconnects ringing current at armature 87, lochs itsell' energized at armature 82 to earth on armature 8?) oi relay 3t) and connects the calling line through condensers to the called line at armatures 8'7 and 68. Current is then led through relay l9 to the called subscribers loop for speaking purposes, while relay t? at armature I00 connects earth direct to'wiper'63 so as to maintain tliel'ine engaged. @onversation can then be carried on in the usual way, while the release is under the control of the calling subscriber, who, on hanging up his receiver, effects the deenergization of relays 28,

47 and 49, when the circuit of magnet 50' is closed as before described, by means of the wiper 74-. until the normal position is reached. It will be obvious that the operations are similar it other numbers were dialled, fol-instance, if number 16 was dialled the only difference in operation would be that when the relay 45 fell back after the second digit, a circuit would be closed through the out Oh relay of the party required or from earth on the private wiper, whereas in the case described, where the second digit was 0, no circuit at all could be closed and consequently the stepping magnet could respond to further impulses.

Again if" the number 8 had been dialled, the operation would have been identical except that the relay would not have been energized and the wipers 58, and would have been used in place oi? the wipers (31. 62" and 63 described.

It the number had been greater than 9, it would have been prefixed by 0, the contacts corresponding to 0 being dead. These points will be well understood by referring to the numbering scheme shown in Figure "he number 100 has been allocated for exchange lines of which up to tour may be fitted on the lower bank, all available positions being taken up on the upper bank.

For a small exchange such as is contemplated by the present invention it is desirable that while certain subscribers have exchange facilities, other subscribers should be barred from getting access to'thetrunlc lines. Let us assume that" substation A; desired to obtain access to atrunk line and for that purpose dialled the number 100, it will also be assumed that this substation was not allowed exchange facilities and in order to ensure this, the contact in the bank wiped over by auxiliary wiper 8a of the finder switch it corresponding to substation A iart'hed. Consequently when the wiper 51 of connector C reaches the 22nd contact vhich it doeswhen the-number 100 is dialled a circuit is closed asfollows, ea-rthed battery on wiper 51, armature of relay 53 and its working contact, relay 65, conductor'SG; armature 87 of relay 19 and its working contact, wiper S l to earth. A circuit is also closed through relay 83, and resting contact ot armature S8 of relay l7 and said armature to earth; the operation of relay Sills without any material effect at this time,

while relay 65 atarmature 89 breaks the restoring circuit through magnet 50' and at armature 6st substitutes earth forthe wiper (53. Obviously, this will beequiyalent to the wiper 63 coming into engagement with a busy line and consequently relay 49 as previously described, is energized" and locks energized to give the busy signal signifying to the calling party that he cannot obtain the connection. 7

Relay 53, as before, is deenergized on the release of the connection, and consequently relays (35 and are also deenergized when this occurs, so that earth is replaced on the endcontacts, wiped over by wiper'i'l, which earth was temporarily removed by armatures 9O, 91', and 93 of relay 33 for a purpose now to be described.

It substation A had been permitted access to exchange lines, there would be no earth on the contact corresponding to that station wiped over by wiper Set of finder switch B and for the purpose of this de scription, it will now be assumed that this is the case. Consequently, when wiper 51 comes into engagement with contacts connected to battery, relay 65 would not energize but relay 33 would. It'the first er'ichange line is free a circuit closed as follows: on the decnergization of series relay after the transmission of impulses earthed battery, relay 9%, 22nd contact in bank swept over by wiper (33, resting contact of arn1a ture til and said armature, working contact of armature '57 and said armature, armature G6 and its resting contact, upper winding of relay l7, armature T1 and its resting contact, armature 31 and its working contact to earth. it will be appreciated that this circuit is substantially identical with that which occurs when a local subscribers line is seized except that the relay 94 is substituted for the cut-off relay of the local subscriber. Consequently, the same sequence of operations occurs assuming that the exchange is of the magneto type, if not, arrangements would be provided so that each exchange line would be called in the appropriate manner, the calling means being set in action by the ringing generator.

The operation of relay 9st connects earth via armature 95 and its working contact, to a common lead connected to the workin contacts of the armatures 90 of relays or the various connector switches in the exchange.

This arrangement is provided so that if the first exchange line called should be en gaged when the number is called the stepping magnet 50 will be automatically energized after the cessation of the diallin to step the wipers round until a free exchange line can be found. The circuit may be traced follows :earth, armature 95 of relay 9a and its working contact, (relay 9% being of course, individual to the trunk line), armature 90 of relay 33 and its working contact, contact 96, wiper 74, interrupter springs" 75, resting contact of armature 89 and said armature, series relay a5, resting contact of armature 4:6 of relay 4'7 and said armature, armature as and its resting .contact or armature 70 and its working contact, stepping magnet 50 to battery. Consequently, series relay a?) will be maintained operated and magnet 50 will automatically make an ad ditional step; if the next exchange line is also engaged, a similar circuit will be closed via armature 97 of relay 98 and its work ing contact, armature 91 and its working contact to contact 99 and wiper 74 from where the circuit continues as before. The consequence is, that the series relay 45 will not deenergize and the magnet 50 will be continiuuisly operated until an idle line is found. On an idle line being found, the magnet 50 will cease to operate and relay 45 will deenergize to close the circuit of the upper winding of relay 47 and the relay of the selected line corresponding to relays 94 and 9S. Relay at? locks energized and connects earth direct to wiper 63 by means of armature 100. The operation indentical with that described above. I

If all the exchange lines should be engaged, it will be noted that no armature is provided to the last relay 101, so that the last contact in the bank wiped over by wiper 74 will not be earthed, even if the line corresponding to it is busy.

On the other hand, as the line is busy the wiper 63 will be earthed, and so the busy tone will be sent back to the calling subscriber similarly to what occurs in the case of a local line which is found to be engaged.

If it is desired that conference facilities shouldbe provided, the number 004: should be allocated for this purpose. An impedance 102 is placed across the line contacts wiped over by wipers 58 and 59 while a permanent potential is placed on the corresponding private contact 103 by means of battery fed through a resistance 10 i, individual to the connector. The consequence is, that the line is always accessible and as many people may confer as there are connectors in the system.

It will be appreciated therefore, that a comparatively cheap and inexpensive small exchange system has been evolved, utilizing apparatus already used in connection with larger exchanges and capable of providing numerous facilities. At the same time it should be appreciated that the invention is not limited to the particular apparatus described, nor to the circuitsshown, as considerable modifications may be made therein without departing from the spirit of the invention as set forth in the appended claims. I

aving now particularly described and ascertained the nature of my said invention, and in what manner the same is to be performed, I declare that what I claim is 1. In an "automatic telephonesystem, two groups of subscribers lines, two link circuits at the exchange, a finder switch at one end of one link circuit having access to the lines in only one of said groups, a finder switch atone end of the other link circuit having access to the lines in the other group but not to the lines in. the first group, and a connector switch at the opposite end of each. link ci cuit, and wipers for each connector having access to all the lines of both groups and having movement in one direction only.

2. In a branch exchange, a line finder connector link for connecting calling and called lines, main exchange trunk lines accessible to said connector, some of the subscribers lines being denied access to said.

trunk lines, a relay in said connector for preventing connection with one of said trunk lines, and a circuit for said relay including a wiper of said finder.

3. In an automatic switch, two sets of wipers, line contacts accessible to one set of wipers and nun'ibered from 2 to 9, correspondingly positioned linc contacts accessible to the wipers of the other set and munbered from 11 to 18, and a wiper switching contact located ahead of the first contact in the second set.

4t. In an automatic switch, two sets of wipers, line contacts accessible to the wipers of one set, similarly numbered line contacts accessible to the wipers of the other set, the second set of line contacts being displaced a distance of one contact with respect to the l'li) wipers, a wiper selecting relay, stepping mechanism responsive to impulses delivered lto said switch to advance both sets ofwipers s l ni iltaneo usly, and a circuit forsaid relay closedby one of said wipers when advanced from normal position.

.6. In an ,automatic switch, two sets of wipers, wiper selecting mechanism, operating mechanism in said switch for advancing said wiper sets simultaneously in a plurality of stages, and a circuit for controlling ,said selecting mechanisinclosed by one of said wipers in the first stage of its operation.

7. In ,an automatic rotary switch of the adding type, two sets of wipers, mechanism foradvancing said wiper sets simultaneously in a plurality ofseparate movements, each movement comprising; one or more steps of equal length, and wiper selecting {mechanism controlled by a wiper ,in one of saidsetsinthe first movement thereof.

.8, Inan automatic rotar switch of the adding type, two sets of wip ers, oneset be ingnormally connected for use, means for advancing vsaid wiper sets simultaneously in aplurality of separate movements, each movement comprising one or more steps of equal length, a wiper switching relay for disconnecting said one set of wipers and for connecting-the other set, and a circuit for said relay closed by a wiper in one of said sets upon the first movement thereof provided the first movement comprises a particular numherof steps. a

S). In .a branch exchange, a link circuit for connecting" calling and called lines comprising a linelinder and a connector, main exchange trunk lines accessible to said connector, some of said subscribers lines being denied access-to saidtrunk lines, a service restricting wiper in said finder, contactsas sOQiated with said} wiper connected to a source of current or not connected at all, depending on whether the corresponding lines are denied access-to saidtrunk lines or not, and means in said connector controlled by said wiper for preventing connection with said trunk lines.

Signed by me at Liverpool, England, this flOth .dayot December, 1920.

JOHN SAVIN. 

